Superhydrophobicity or Lotus Effect is the ability of a surface to repel water completely by making them to roll off from the surface. Different surfaces have different contact angles with water. Normally, normal hydrophobic surface has contact angle of about 90-120° with water drops. On such surfaces water can form a semi spherical drop instead of uniformly wetting the surface, but still need a large tilt to roll them off the surface. However, certain metallic or polymer surfaces can be tailored to achieve the contact angle of more than 150° with water and known as super hydrophobic surface. On such surfaces water can form a perfect spherical drop and can be rolled off even on the horizontal surface. The best example of a super hydrophobic surface can be found in the nature. There are hundreds of plant leaves including lotus leave, that show superhydrophobicity. Mimicking such mechanism on metal, alloy, composite or polymer surface can find a lot of applications in the areas of airplanes, automobiles, electronics, etc.
One such important application is in the area of aerospace industry. Ice formation on the body of airplanes poses several problems like increasing drag and decreasing lift. Very thin ice sheets on leading edges of airplane airfoils can reduce the lift as much as 30-40% [1]. Ice can also cause engine stoppage due to its accumulation on carburetor and the engine's air source. Hence it is very important to protect the surface of the airplane and other crucial parts from the accumulation of ice. While there are many ways of avoiding ice formation, such as keeping the airplane body surface always above 0° C., most of the times it is not practical since it is difficult to maintain the heat on all parts of the body. Hence making airplane body surface super hydrophobic may save a lot of money and energy, and more importantly, improve the safety of airplanes.
There are many ways of achieving the super hydrophobic surface. Water is a polar solvent and hence if a surface can be modified into polar surface, then water can easily repel from the surface. However, such surface modification is not always straightforward. In addition, the reliability of such treated surfaces is not guaranteed under extreme conditions. Rough surfaces with different micro texture have shown high water repellent behavior. There are many ways of modifying surface texture and many references can be found in literature. In fact, a near perfect super hydrophobic surface with a contact angle of 178° has been achieved. However, such surfaces still lack the ability in terms of sustainability under extreme weather conditions such as icing conditions.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.